Motor-control system



June 26, 1923.

R. E. HELLMUND MOTOR CONTROL SYSTEM 2 Sheets-Sheet 1 FiledOct. 8. 1918 ATTORNEY 0 R m M Mfi 5 M m n WITNESSES: $46M paw/aw Jun 26, 1923.

R. E. HELLMUND MOTOR CONTROL SYSTEM Filed Oct. 8, 1918 2 Sheets-Sheet 2 W II IIL. L

QLEET INVENTOR f-Pua/o/f heflmund.

ATTRNEY Patented June 26,

UNITED. STATES 1,460,157 PATENT oFncE;

BUlbOLI' E. HELLMUND, OF BWISSVALE, PENNSYLVANIA, ASSIGNOR TO WESTING- HOUSE ELECTRIC & IANUFACTURING COMPANY, A CORPORATION OF PENNSYL- VANIA.

iro'ron-con'rnor. srs'rmr.

Application flied October 8, 1918. Serial 1T0. 257,348. I

To all whom it may concern: I Be it known that I Rooonr E. IIELIr MUND, a citizen of the (irerman Empire, anda resident of Swissvale in the count of 5 Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Motor-Control Systems, of which the following is a speclfication.

My invention relates to control systems for alternating-current motorsand particularly to systems for effecting changes of ponnections of the motor windings to the In the operation of starting induction motors it is customary first, to subject the primary windings of the motor to a reduced voltage by connecting the motor to the line if the motor is carrying a load, does not rotate with synchronous speed but with the somewhat lower speed of the rotor. At the moment of reclosing the primary clrcuit,

therefore, it may occur that the primary and the secondary windings are of opposite polarity, causing excessive currents and the well known inconveniences attendant thereupon; This effect may be avoided by accomplishing the transition from low to 40v high voltage without disconnecting the motor from the line.

Again, in the operation of adjustable tor motors in which it is desired that, at no moment, shall the motor be out of the positive. controlof the operator and in gear drives in order to avoid. mechanical shocks and consequent damage to the gears and other parts.

My invention has for its object to provide a novelv control system by means of which many such changes may be effected without disconnecting the motor or other translating device from theline. It is another object of my invention to accomplish this with a minimum number of switches and control devices. Accordingto my invention, the circuit transition is efl'ected by changing each phase individually from the one voltage to the other, so that at least one phase is always closed and the proper phase relation between the motor and the line thus always maintained.

My invention has the further advantage that the transition is accomplished without loss of torque.

- For'the purpose of explaining my invention, I have herein illustrated it as employed first, in connection with a starting system for induction motors and secondly, in connection with a 2-speed induction motor, the primary windings of which are arranged for series and parallel star connections. It will be understood, however, that my invention is of more general application, applicable alike to induction motors and to motors of the polyphase commutator type and that the described embodiments are illustrative purely.

In the accompanying drawings, Figure 1 is a diagrammatic view of a starting system for an induction motor, the control circuits being arranged according to my invention; Figs. 2 to 9 are diagrammatic views of the circuits illustrating the'sequence of operations; Fig. 10 is a diagrammatic view of a 2-speed induction motor having my invention applied thereto and Figs. 11 to 18 are views similar to Figs. 2 to 9.

Referring particularly to Figs. 1 to 9, line conductors 1, 2 and 3 of a three-phase transmission line, which may be connected to any suitable source of .electrical energy, supply current to the primary windings 4 of an induction motor 5, either of the s uirrel-cage, or of the wound-rotor 't T e windin 4 are shown as connecte to the line con uctors 1, 2 and 8, b conductors 6, 7 and 8,.through the me um ofa transformer 9 having three legs 10, 11 and 12. In the process of starting the motor, the conductors 6, 7 and 8 are connected to the line conductors 1, 2 and 3 first, through the transformer 9, at the intermediate points 13, 14 and 15 of the legs of the transformer, and later, directly to the conductors 1, 2 and 3at 16, 17 and 18, respectively. Switches 21, 22 and 23, of the electromagnetic, camoperated or any other" desired type, serve to connect the line conductors 1, 2 and 3 to the legs of the transformers 10, 11 and 12. The connections of the motor conductors 6, 7 and 8 to the intermediate points 13, 14 and 15 of the transformer may be efiected by means of switches 24, 25 and 23. The ultimate connections to the line maybe efiected through the switches 27, 28 and 29. I have herein illustrated these switches as of the electromagnetic type, the circuits of the coils of which are closed by a drum controller 30.

The operation is as'follows: The switches 21 to 26 will be closed in the first position of the controller 30 to connect the primary windings 4 to the line conductors 1, 2 and 3 at low voltage through the transformer 9. The connections are as illustrated in Fig. 2. Upon moving the controller to the second position, the switch 24 will be opened, resultmg in the connections diagrammatically shown in Fig, 3. A movement of the controller another ste will cause the closing of the switch 27, with the consequent resulting connections shown at Fig. 4. Two of the phase windin s of the motor are now connected to the hue at low voltage and one at high. 'Similarly, successive actuations of the controller will cause the opening of the swltch 25 (Fig. 5), the closing of the switch 28 (Fig. 6), the opening of the switch 26- 7) and the closing of the switch 29 Flg. 8). The motor is now in parallel with the transformer 9.. In the last position of the controller, the switches 21, '22 and 23 are opened resultin in the connections illustrated at Fig. 9, the motor being directly connected, at high voltage, to the line conductors 1, 2 and 3 and the transformer 9 being disconnected therefrom.

I thus provide a means for changing the connections of the motor-winding conductors from the mid-points of a multi-phase transformer wlnding to the terminals thereof without at any time completely severing the connectlons.

In Figs. 10 and 18', I have illustrated my invention as applied to a two-speed induction motor 5, the primary windings 4. of WhlCh, having legs 10, 11 and 12, are arranged for series and parallel-star connec tions. The switches 24,25 and 26 are adapted to close to connect the motor to the hue conductors 1, 2 and 3 for low-speed operation; The switch 27 may be closed to connect an intermediate point 14 of the leg 10 to the line conductor 1 through an inductive winding or other impedance 31. This winding may be short-circuited by a switch 32 after the danger of short-circuiting a portion of the windings 4 has been eliminated. The switch 28 may be closed to connect an intermediate point 13 of the le 11 to the line conductor 2. I thus provide for reversin the phase relations of the legs 10 and 11. e switch 29, upon closing, connects an intermediate point 15 of the leg 12 to the line conductor 3. The switches 33 and 34 may be closed to connect the terminals of the legs 10, 11 and 12 to a second star point,

The drum controller 30 is diagrammatically illustrated as closing, in its first position, the switches 24, 25 and 26 to connect the windings 4 in series-star relation, and the 'motor, therefor, for low-speed operation (Fig. 11).

To effect the transition changes from highspeed operation, the controller is first ac'tuductor 1 and the intermediate point 14 of,

the leg 10 is connected thereto through the inductive coil 31. The use of the coil 31 avoids a near short-circuit while the terminal of the leg 10 is connected to the line conductor 2 and its mid-point 14 to the line conductor 1. The next operation of the controller causes the opening of the switch 25 and the consequent disconnection of the leg 10 from the line conductor 2 (Fig. 14), and another -ste through the closing of the switch 28, t e connectin conductor 2 of the intermediate point 13 of the leg 11, (Fig. 15). The next position of the controller causes the closing of the switch 32 to short-circuit the inductive winding 31, and still another step, by 0 ning the-switch 26, the disconnectin o the le 12 from the line conductor 3. l(ls ig. 16) Tfie next operation of the oontro er causes the closing of the switch 29 (Fig. 17 The terminal points of the legs 10, 11 and 12 are now disconnected from the line conductors 1, 2 and 3 and the intermediate points 13, 14 and 15 are connected thereto with a phase reversal between the le 10 and 11. The last oint of the control or causes the closing 0 the switches 33 and 34 to efiect the parallel-star connection of Fig. 18.

The changes of connections are thus effected for one phase winding at a time without, at that time, o ening the circuits of. the other phase win ings, which results in effecting the transition without loss in torque.

The connection above described may obviously be effected in the reverse order when desired.

iii

I claim as m invention 1. The combination with a two-speed induction motor having star-connectedphase windings, and a source of electrical energy therefor, of means for connecting said motor the phase windings 0 said motor to operate said motor at 'a second speed. a,

, 2. The combination with a two-speed induction motor having star-connected phase windings, and a source of electrical energy therefor, of means for connecting said motor to said source for o eration at one speed means for reversing t e phase sequence 0% two of said phase windings, and means for successively changing the connections of the phase windings of said motor to operate said motor at a second speed while maintaining a circuit from Fflld source through portions of two of said phase windings.

3. The method of operating a polyphase motor having star-connected phase windings, which consists in connecting the terfminals of each of said windings toasource of electrical'energy, successively disconnecting the terminals of said winding from said source, connectin an intermediate point of each of said win ings to said source in such manner as to reverse the phase sequence of two of said phase windings, and connecting the terminals of said-phase windings to a 35, common point.

4. The method of operating a polyphase induction -motor havingv star-connected windings, which consist in successively Y disconnecting certain of said phase windwindings from sai 'from sai ings from said source, reconnecting an intermediate point of each of said phase windings to said source in such manner as to reverse the phase sequence in said windings and to maintain a circuit from said source through portions of at least two of said phase windings during said transition, connectin an intermediate point of a third of said p ase windings to the source of energy, and connecting the terminals of said windings to a common point.

5. The method of operating a polyphase motor having star-connected windings, which consists in connecting the terminals of said windings to a source of polyphase electrical energy, disconnectin one of said phase source, connecting one terminal of an impedance device to the phase from which said first named windings is disconnected and the other terminal of ,said device to an intermediate point of a second ofsaid phase windings, disconnecting said second winding from said source, connecting the intermediate point of said first named phase winding to the phase of said source from which said second phase winding is disconnected, bridging said impedance device, disconnectin a third of said phase windings source and connecting an intermediate point of said third phase winding to a third phase of said source, and connecting the terminals of said phase windin s to a common int.

n testimony w ereof, I have hereunto subscribed by name this 30th day of Sept,

RUDOLF E. HELLMUND. 

